水下扇岩相特征及形成机制

２０世纪５０年代初期以来，沉积物重力流研究得到沉积学家们的广泛重视，特别是自６０年代末期，与沉积物重力流密切相关的水下扇研究成为沉积学领域的热点。通过对国内外大量沉积物重力流及水下扇研究成果的总结，结合我国中新生代陆相断陷盆地水下扇发育的特点，将水下扇的组成岩相划分为基质支撑砾岩相、颗粒支撑砾岩相、砾质砂岩相、块状砂岩相、经典浊积岩相。水下扇的形成机制系重力流成因。内扇以杂基支撑、颗粒支撑砾岩组合为特征；中扇以砾质砂岩、块状砂岩组合为特征；外扇以ＣＤＥ序及ＤＥ序经典浊积岩发育为特征。

三峡水库水环境与水生态研究的进展与展望

伴随着举世瞩目的三峡工程全面竣工,三峡水库于2010年正式进入年水位落差达30 m的正常运行阶段.水库湖沼学可为环境友好型大坝建设和水库可持续管理提供科学依据.本文在三峡成库8 a以来生态系统长期监测与研究的基础上,对三峡水库水环境现状进行了归纳和总结,分析了水环境动态的时空异质性、水库纵向分区与群落组成、垂向分布及藻类水华的成因和动态,并对三峡水库藻类水华预警与生态-水文调控机制展开了论述.最后,本文尝试给出以下两方面的展望:1)大型水库湖沼学观测研究应有长期的策略;2)近期研究应重点关注水华暴发水动力学机制的量化和水华预警模型及生态水力调度平台的耦合.

Dynamic simulation and optimal control strategy for a parallel hybrid hydraulic excavator

The primary focus of this study is to investigate the control strategies of a hybrid system used in hydraulic excavators. First, the structure and evaluation target of hybrid hydraulic excavators are analyzed. Then the dynamic system model including batteries, motor and engine is built as the simulation environment to obtain control results. A so-called multi-work-point dynamic control strategy, which has both closed-loop speed PI (proportion integral) control and direct torque control, is proposed and studied in the simulation model. Simulation results indicate that the hybrid system with this strategy can meet the power demand and achieve better system stability and higher fuel efficiency.

CFD prediction of local scour hole around bridge piers

In order to predict the local scour hole and its evaluation around a cylindrical bridge pier, the computational fluid dynamics （CFD） and theories of sediment movement and transport were employed to carry out numerical simulations. In the numerical method, the time-averaged Reynolds Navier-Stokes equations and the standard k-e model were first used to simulate the three-dimensional flow field around a bridge pier fixed on river bed. The transient shear stress on river bed was treated as a crucial hydrodynamic mechanism when handling sediment incipience and transport. Then, river-bed volumetric sediment transport was calculated, followed by the modification of the river bed altitude and configuration. Boundary adaptive mesh technique was employed to modify the grid system with changed river-bed boundary. The evolution of local scour around a cylindrical bridge pier was presented. The numerical results represent the flow pattern and mechanism during the pier scouring, with a good prediction of the maximum scour hole depth compared with test results.

Effects of Low Concentration Methanol, PVP and PVCap on Structure-I Methane Hydrate Formation

Kinetic mechanisms describing how THIs （thermodynamic hydrate inhibitors） and KHIs （kinetic hydrate inhibitors） work on gas hydrate formation have drawn interests for decades. These mechanisms could be better revealed with more fundamental experimental studies. With experiments performed in an isochoric cell with continuous cooling and stirring, this paper presents observed effects of methanol, PVP （polyvinylpyrrolidone, Mw= 15,000） and PVCap （polyvinylcaprolactam, Mw = 6,000） on both nucleation and growth of structure-I methane hydrate at concentrations 100 to 3,000 ppm （i.e., 0.01 to 0.3 wt%）. The results suggest that methanol had no significant effect on nucleation, while it weakly promoted, spontaneous hydrate growth at an early stage. PVP and PVCap gave reduced average nucleation rate at and prior to hydrate onset, while increased the induction time and the degree of sub-cooling. PVP gave no observable effect on total gas intake and average hydrate growth rate. A decreased total gas intake was observed for all concentrations of PVCap.

Molecular dynamics simulations of the mechanisms of thermal conduction in methane hydrates

The thermal conductivity of methane hydrate is an important physical parameter affecting the processes of methane hydrate exploration,mining,gas hydrate storage and transportation as well as other applications.Equilibrium molecular dynamics simulations and the Green-Kubo method have been employed for systems from fully occupied to vacant occupied sI methane hydrate in order to estimate their thermal conductivity.The estimations were carried out at temperatures from 203.15 to 263.15 K and at pressures from 3 to 100 MPa.Potential models selected for water were TIP4P,TIP4P-Ew,TIP4P/2005,TIP4P-FQ and TIP4P/Ice.The effects of varying the ratio of the host and guest molecules and the external thermobaric conditions on the thermal conductivity of methane hydrate were studied.The results indicated that the thermal conductivity of methane hydrate is essentially determined by the cage framework which constitutes the hydrate lattice and the cage framework has only slightly higher thermal conductivity in the presence of the guest molecules.Inclusion of more guest molecules in the cage improves the thermal conductivity of methane hydrate.It is also revealed that the thermal conductivity of the sI hydrate shows a similar variation with temperature.Pressure also has an effect on the thermal conductivity,particularly at higher pressures.As the pressure increases,slightly higher thermal conductivities result.Changes in density have little impact on the thermal conductivity of methane hydrate.